1. Field of the Invention
The present invention relates to railroad hopper car construction, and more particularly relates to the construction of a bolster assembly for supporting the overhanging end hopper compartments at opposite ends of the car.
2. Description of the Prior Art
Railway hopper cars are generally constructed having a series of adjacent hopper compartments defined by arcuate or curved side sheets and subdivided internally by bulk heads having an inclined portion. Slope sheets are provided at opposite car ends. Bottom hopper outlet adapters are arranged beneath the car for the discharge of lading material from the compartments. The outlet adapters are located so that the inclined bottom portions of the individual compartments funnel the material into the discharge opening.
According to conventional construction, an end support structure is secured to the end slope sheets at opposite ends of the car. The end structure serves to support the hopper car construction and to receive the draft gear coupler structure and the truck coupling. The end structure is designed to withstand buff and impact loads exerted at the coupler during operation of the hopper car. It is also designed to transmit the vertical load imposed by the car body and cargo.
Various conventional end structures are known in the art, for example as disclosed in U.S. Pat. No. 3,339,499. This patent discloses a covered hopper railway car having a bolster assembly extending between the side sills at either end of the car near the bottom of the slope sheet. The bolster assembly includes a lower cover plate and an upper generally horizontal shear plate. An end or center sill assembly receives a draft gear and coupler structure. A pair of diagonal end struts or gussets extend between the shear plate and end sheet, converging inwardly from the end sheet to the shear plate.
Various modifications to this prior art structure are known. For example, U.S. Pat. No. 3,490,387 discloses a covered hopper car construction utilizing diagonal struts or gussets as described above and further shows the use of a substantially vertical transverse web member extending between the end slope sheet and center sill structure inward of the diagonal gussets. In this construction, the stub center sill is longitudinally spaced from the end slope sheet thereby forming an open type torque box wherein loads transmitted through the stub center sill, shear plate, bolster web and slope sheet are taken up by the diagonal gussets which extend between the slope sheet and the shear plate.
Yet another railway hopper car end structure is disclosed in U.S. Pat. No. 3,844,229 in which the end supporting structure includes a bolster assembly having a bottom plate extending transversely between the side sills and an upper arcuate wrap sheet secured at the opposite side sheets and at the inclined slope sheet. Diagonal gusset plates and vertical web plates extend between the wrap and bottom sheets to strengthen the assembly. A plurality of generally semicircular diaphragm plates extend transversely between the wrap sheet and the slope sheet at locations above the car axis and the center plate to structurally stiffen the car body.
Because of the expense associated with the fabrication and assembly of a railway hopper car, there is a continuing interest in providing hopper car construction which is highly effective for accommodating operational loads while being relatively simple, lightweight, and having a minimum of structural elements. According to known prior art approaches, the through center sill has been eliminated in favor of the stub center sill and the side sills have been elevated relative to the stub center sill in order to reduce the height of the arcuate side sheets. The use of the stub center sill permits unobstructed hopper discharge. Utilization of the high side sills permits a substantial reduction in the size and weight of the arcuate side sheets. However, because of the difference in the elevation of the draft stub center sill and the side sills, a moment arm exists between the center line of the coupler and the shear plate. Because of this misalignment, the end of the car and the stub center sill is subject to a rotational moment which tends to force the assembly downwardly or upwardly upon the exertion of draft or buff forces against the car. This moment must be reacted by the end support structure to prevent structural damage. Therefore the end support structure must satisfy the functions of reacting the induced moment caused by the difference in elevation between the side sills and the stub center sill, it must distribute the load of the car and of the lading uniformly to a truck assembly upon which it rests, and it must distribute the draft and buff forces received through the coupling mechanism uniformly throughout the car and avoid concentration of stress. Also, it must react torsional forces applied to the coupling mechanism.